Telephone system



Aug. 26, 1930; .J. E. OSTLINE ET AL 1,174,335

TELEPHONE SYSTEI l l l l Jim-rim Jul-m Elli: UFflina mas El? mar 35Thomas Phili u FEET Filed Nov. 21. 1927 5 Sheets-Sheet 1 7 Aug. 26,1930.

J. E. OSTLINE EIAL 1,174,335

TELEPHONE SYSTEM Filed Nov. 21, 1927 5 Sheets-Sheet 2 Jul-m EllisUFH'II'LI Thnmas HE: Thomas F Aug 26, 1930. a. ELOSTLINE ET A1. I1774.335

TELEPHONE SYSTEI 's'iied $114,, 1927. s Sheets-Sheet 4 FLY +H Juhn E111:UFHme Roma: ngr

Thqmas FEE Fm J. E. :QSTLINE 7ET AL 1,774,335

TELEPHONE SYSTEM Aug. '26, 1930.

iled Nov. 21,1927 5 sneak-shee s Jul-m EH15 [IF [line Thomas Rfia nerThomas Phil 1 PF? Patented Aug. 26, 1930 UNITED STATES PATENT OFFICEJOHN ELLIS OSTLINE, THOMAS a. RAYNER, AND THOMAS PHILIP PREIST, orLIVER- POOL, ENGLAND, ASSIGNGRS TD ASSOCIATED TELEPHONE AND TELEGRAPHGOM- 1 ANY, or KANSAS cIrY, MISSOURI, A coBPoRATIoN OF DELAWARETELEPHONE SYSTEM Application filed November 21, 1927, Serial No.234,608, and in Great Britain March 2, 1927.

The present invention relates to telephone systems and is moreparticularly concerned with arrangements for notifying a calling partyof the busy condition of a line or group of lines which has beenencountered in the setting up of a connection. The problem to be solvedis that the signalling condition must be such as to give a tone in casethe calling party is a subscriber and also to provide a special currentfor operating a flashing signal in case the calling party is anoperator. This latter requirement has been met by arranging for thealternate connection of battery and earth to one speaking lead throughthe winding of the line relay and in these circumstances the line relaywill release at the time a simplex battery connection is made.Accordingly arrangements must also be provided, conveniently bycompleting an alternative circuit for the usual release relay, toprevent the connection from being cleared down during this interval. Ithas also been usual in the past to superimpose the busy tone on thespecial connection to one speaking lead as this simplifies the circuitsand reduces to a minimum the number of common leads re quired. It isfound, however, that when the busy tone is provided in suflicient volumeto transverse long junction lines, considerable overhearing or crosstalk is apt to occur owingv to the fact that the tone is appliedtooneleg only and hence owing to the various bridges across theline, thereturn tone current is by no means equal to that originally applied. Thepresent invention aims at overcoming these disadvantages by applying thetone in such a fashion as to secure complete balance at all times andthus eliminating the detrimental eifects of overbearing which it will beappreciated might constitute a serious disadvantage.

According to one feature of the invention, this object is attained inthat the two speaking leads are adapted to be connected respec tively toopposite sides of the busy tone source at the switch at which the busycondition is encountered so that the tone is applied ina loop circuit.

According to another feature of the invention, the busy tone source isadapted to be connected without battery or earth connections across thespeakingleads at the switch at which the busy condition is encounteredwhich means that leakage which might give rise to overbearing is almostentirely prevented, I

In order that the principles of the inven tion may be betterappreciated, various arrangements for carrying it into effect will nowbe described by way of example, reference being had to the accompanyingdrawings. I

Fig. 1 shows a well-known arrangement for applying busy tone to acalling line from a connector switch. Fig. 2 shows an arrangement forapplying a busy tone to both speakingconductors of a calling line inseries. Fig. 3 shows an arrangement for applying a busy tone to bothspeaking conductors of a line through the windings of the line relay.

Fig. 4 shows an arrangement somewhat simi-,

lar to Fig. 3 except that the tone is applied to the line conductorsthrough resistances instead of through the windings of the line relay.Fig. 5. shows the arrangement of Fig. 1 modified for use with a selectorswitch. Fig. 6 is a modification of Fig. 2 as applied to a selectorswitch. Fig. 7 shows an arrangement for applying busy tone to a linethrough an auxiliary winding of the line relay. Fig. 8 shows anotherarrangement for applying busy tone to a line from a selector. Fig. 9 isa modification of Fig. 3 showing a method of reducing the number ofconductors between the individual switches and the common toneapparatus.

Referring first to Fig. 1 this shows in schematic form one arrangementwhich is at present employed, this arrangement being open to certain ofthe objections mentioned above. Reference numeral 1 repersents thetransmitter as typical of the substation, and 2 is the line relay whichsupplies feeding current. The high impedance relay 3 is connected acrosstheline in known manner in series with the polarized relay 4 which isused for effecting metering or giving supervisory signals. The linerelay of a connector switch is indicated by 5, and 6 is the releaserelay which is energized over its top wind- III ing when the line relayis operated. In the case of a connector a busy condition will only arisein case the line of the party desired is found busy and in this casecontacts 7 and 8 carried by the busy relay will be operated. Theequipment enclosed in the dotted rectangle is common to a number ofswitches and comprises the busy tone transformer BT, and the interrupterrelay 11 which is energized and deenergizes periodically, for instanceevery 1 seconds, by means of the interrupter contact 12. will be seenthat after contacts 7 and 8 are operated and while relay 11 is notoperated, battery will be connected to the lower speaking conductorthrough the lower winding of line relay 5 and battery will also beconnected through the lower winding of release relay 6 to maintain thisrelay operated. lVhen the interrupter contacts 12 next close, relay 11is operated and thereupon at armature 9 busy tone is connected up andthe holding circuit for relay 6 is opened so that if the subscriberhangs up at this time the connection will be released. It will be seenthat the busy tone is applied to one lead only and the return circuitmay be by way of either relay 2 or relay 5 so that a certain amount ofunbalance is produced and overbearing is likely to occur. This can bereduced to some extent by connecting the junction of the winding ofrelay 5 and the upper speaking lead to earth through a suitablecondenser.

In the more completely satisfactory arrangement shown in Fig 2 however,the trouble is overcome in that the busy tone from the transformer ET isapplied to both speaking leads over the operated armatures 16 and 17 ofthe busy relay. Armatures 15 and 18 can ried by this relay performs thesame functions as in the arrangement shown in Fig. 1 and as before theinterrupter relay 22 operates the armatures 19, 20 and 21. In this case,the busy tone circuit is independent of the circuit over armature 15 bywhich battery and earth are connected alternately to the lower windingof line relay 14. Each connector is provided with a busy tone condenser23 which, together with the common busy tone condenser 24, serve toprevent interference between lines connected to the common toneapparatus simultaneously.

In the arrangement according to Fig. 3, the busy tone instead of beingapplied directly to the speaking leads as in the arrangement shown inFig. 2 is supplied through both windings of the line relay 23 and theconnection of battery to the middle point of the secondary of thetransformer BT for the flashing signal ensures that complete balanceshall be obtained at all times. It will be understood that armatures 24,25 and 26 are again carried by the busy relay.

In Fig. at a somewhat different arrangement is employed in that busytone is now applied to the two speaking conductors through theresistances 31 and which may conveniently have a value of approximately50 ohms. In this case the line relay 30 held up during the applicationof the flash battery owing to the local circuit which is then completedfor its lower winding. Consequently since relay 30 does not deenergizeat any time there is no necessity for the provision of a holding circuiton the release relay and thus the number of common leads can be reduced.

The problem of giving busy from a selector switch is substantially thesame though in this case instead of the necessary circuit changes beingeii'ected by a busy relay, they will be brought about by cam springswhich are operated when the sw"ch moves to its all trunks busy position.Figure 5 shows diagrammatically an arrangement at present employed forgiving busy from a selector, and it will be appreciated that it issubstantially the same as that shown in Figure 1 covering the case of aconnector. The springs 42 and l3 in Fig. 5 are however cam springs andduring the application of busy flash battery, relay to is deenergizedwhile release relay L1 is at this time energized over the specialholding circuit. As pointed out in connection with Fig. 1 theapplication of busy tone is in this circuit to one lead only.

The arrangement shown in Fig. (3 is substantially similar to that shownin Fig. 2, though in this case the springs 45, 1G and 47 are cam springsrather than arniatures on a relay. Moreover the connection of the leadsthrough which the busy tone is fed will be made not to the actualspeaking leads but to the leads extending to the windings of the linerelay over back contact-s carried by the switching relay since thisrelay is not operated when the switch mores to the eleventh rotaryposition. Armatu o 8, 49 and 50 are, it will be understood, carried bythe interrupter relay, and 51 is the usual release relay for which ahoidin circuit is completed through its lower wn lingduring the timethat busy flash battery is being applied.

A modified arrangementi iown in Fig. 7, the feature of which is that thebusy tone is not connected directly to the line or to the normalwindings of the line relay but a third winding is provided on the linerelay and busy tone is fed through this whence it is transmitted to thecalling party by induction. Conveniently the circuit for this thirdwinding of line relay 55 may include the second winding on the releaserelay 51, com eniently shunted by a condenser 57, but if desired thecurrent flow through the third winding may be arranged to be sufiicientto hold the line relay energized during the time that current is cut offthrough the usual two windings and in this case no second winding isnecessary for the release relay since its usual circuit will becompleted the whole time the line relay. Springs 59 and 60 it will beunderstood are cam springs operated when the switch moves to theeleventh rotary position. Thisarrangement may be preferable to thatshown in Fig. 6 in that it only requires two common leads as againstfour required with the latter arrangement.

Figure 8 shows a further modification in which only two common leads areused and holding is effected over one of them which also serves for theapplication of the busy flash battery. In this case the lower winding ofline relay 61 is connected to the associated speaking conductor throughthe resistance 62 and when the cam springs 63 and 64 are operated, busytone is connected up tothe speaking conductors in a circuit which Wlllbe readily followed andwhen the interrupter relay energizes it appliesbattery at armature 6 5 to maintain line relay 61 over its lowerwinding. In this case the interrupter relay also at armature 66 Idisconnects the busy tone by opening the primary winding. of the busytone transformer this arrangement being preferable in some cases.

Figure 9 shows a further modlfication ot Fig. 3 in which only two commonleads are used and the holding is effected over one of the common leads.In this case the busy tone is connected directly to the two speakingleads through the contacts 68 and 69 controlled by the busy relayand thebattery potential connected to the middle point of the secondary windingof the busy transformer ET maintains the line relay 67 energized.

It will be see therefore that according to the invention various noveland improved arrangen'ients have been devised for feeding busy tone in abalanced circuit while at the same time providing facilities forflashing the supervisory lamp at an operators position and preventingany appreciable degree of overhearing.

What is claimed is:

i. In a telephone system including automatic switches for setting upconnections between a calling and a called line, a busy tone source, andmeans operative when a busy line or group of lines is encountered insetting up a connectionfor connecting the busy tone source withoutbattery or ground connections across the speaking leads at the switch atwhich the busy condition is encountered to transmit the busy tone to thecalling line.

2. In a telephone system including automatic switches for setting upconnections bet veen a calling line and a called line, a busy tonesource and a special signalling current, and means operative when a busyline or group of lines is encountered by one of said switches in settingup a connection for trans mitting the special signalling current in thedirection of the calling line and for connecting the two speaking leadsof the switch, re-

spectively, to opposite sides of the busy tone source to transmit a busytone to the calling line.

3. In a telephone system as claimed in claim 2, in which the busy tonesource and special signalling current are applied simultaneously butalternate with normal conditions.

l. In a telephone system including automatic switches for setting upconnections between calling and called lines, a busy tone source and aspecial signalling current, and means operative when a busy line orgroup of lines is encountered by one of said switches in setting upaconnection for connecting the special signalling current through awinding of the line relay of said switch and for con neoting the busytone source directly to the two speaking leads of said switch.

5. In a telephone system, an automatic switch for extending connectionsbetween calling and called lines, a line relay and a release relay insaid switch, a busy tone source and a special signalling current, meansoperative when a busy line or group of lines is encountered by saidswitch in setting up a connection for connecting said busy tone sourceto the two speaking leads of said switch and for connecting saidsignalling current to a winding of said line relay, and means comprisinga special holding circuit for said release relay to prevent the releaseof said switch in case the line relay deenergizes when said signallingcurrent is connected thereto. I

6. In a telephone system including automatic switches for setting upconnections between a calling line and 9. called line, a busy tonesource and a special signalling current, and means responsive when abusy line or group of lines is encountered by one of said switches fortransmitting the special signalling current in the direction of thecalling line and for transmitting the busy tone from said source overthe two talking conductors of the switch in series.

7. In a telephone system, an automatic switch for extending connectionsbetween calling and called lines, a release relay in said switch, a busytone source and a special signalling current, means responsive when abusy line or group of lines-is encountered by said switch in setting upa connection for applying the busy tone from said source to the twotalking conductors of said switch and for transmitting the specialsignalling current in the direction of the calling line, and means formaintaining said release relay energized during the transmission of saidspecial signailing current.

8. In a telephone system including automatic switches for setting upconnection-s between calling and called lines, a busy tone sourcecomprising a transformer common to all said switches, a condenserindividual to each of said switches and another condenser common to allof said switches, and means responsive when a busy line or group oflines is encountered by one of said switches for connecting thesecondary winding of said transformer to the talking conductors of theswitch in series with said condensers.

9. In a telephone system including automatic switches for setting upconnections between calling and called lines, a busy tone sourcecomprising a transformer common to all of said switches, a condensercommon to all of said switches and a non-talking condenser individual toeach of said switches, and means responsive when a busy line or group o1lines is encountered by one of said switches for connecting thesecondary winding of said transformer to the calling line in series withsaid condensers.

10. In a telephone system, a line comprising two conductors terminatingin an automatic switch, a double-wound li e relay for the switchnormally brid ed across the conductors oi? said line in s with batteryand ground, a busy tone tra .ormer, and means for intermittently bridgi1g said transformer across the conductors or said line and forsubstituting a battery connection for the normal ground connection infirst said bridge.

11. In a telephone system, an automatic switch including a double-woundline relay for ex ending connections to called lines. a bridge includinga busy tone transformer connected across the talking conductors of theswitch responsive to the extension of a connection to a busy line, andan interrupter relay for alternately connecting ground and battery to awinding of the line relay andtor alternately opening and closing saidbridge.

12. In a telephone system including auto- :natic switches ifor settingup connections be tween calling and called lines, a doublewound linerelay for each switch, a common busy tone source, and means operat'vewhen a. bisy line is encountered by one of said switches for alternatelycormecting battery and ground to a winding of the line relay ot' theswitch and for connecting said busy tone source across the talkingconductors to the switch.

13. In a telephone system including automatic switches for setting upconnecti between calling and called lines, a line relay and a releaserelay for each switch, a common busv tone source, and means operativewhen a busy line connected with by one oi? said switches tor alternatelyconnecting bat tery and ground to a winning of the line relay of theswitch, "for comiecting said busy tone source across the talkingconductors of the switch, and for intermittently completing an auxiliaryholding circuit for the release relay of the switch.

14. In a telephone system including automatic switches for extendingconnections between calling and called lines, a line relay for eachswitch, a busy tone source common to all of said switches, meansoperative when a busy line is connected with by one of said switches forconnecting said tone source 1n bridge of the talking conductors of theswitch, and an interrupter relay for intermittently opening and closingsaid bridge. and for alternately connecting battery and ground to awinding of the line relay of the switch.

15. In a telephone system, an automatic switch for extending aconnection between calling and called lines, a line relay in said switchhaving two windings connected to the two speaking leads of said switchand having an auxiliary winding, a busy tone source, and means operativewhen a busy line or group of lines is encountered by said switch inextending a connection for connecting said source to said auxiliarywinding, said auxiliary winding inductively causing a busy tone to betransmitted in the direction of the calling line through the otherwindings of said line relay.

16. In a telephone system, an automatic switch for extending aconnection between calling and called lines, a line relay in said switchhaving two windings connected to the two speaking leads of said switchand having an auxiliary winding, a busy tone source, and means operativewhen. a busy line or group of lines is encountered by said switch inextending a connection for connecting said source to said auxiliarywinding, said auxiliary winding inductively causing a busy tone to betransmitted in the direction of the calling line throu h the otherwindings of main line relay, and for maintaining said line relayenergized independent of the calling line.

17. In a telephone system as claimed in claim 15 including a releaserelay for said switch in which the busy tone source is also fed througha winding on the release relay.

18. In a telephone system, an automatic switch for extending connectionsbetween calling and called lines, a line relay in said switch having twowindings, one or more resistances in said switch, the two speakingconductors of said switch connected to the two windings of said relay,respectively, by way of one or more of said resistances, a busy tonesource, and means operative when said switch encounters a busy line orgroup of lines for connecting said busy source directly to the windingsoi said relay and. to the two speaking leads by way of one or moreresistances in order to transmit a busy tone to the calling line.

19. In a telephone system, an automatic switch for extending connectionsbetween calling and called lines, a line relay in said switch having twowindings, one or more resistances in said switch, the two speakingconductors of said switch connected to the two windings of said relay,respectively, by way of one or more of said resistances, a busy tonesource, means operative when said switch encounters a busy line or groupof lines for connecting said busy source directly to the windings ofsaid relay and to the two speaking leads by way of one or moreresistances in order to transmit a busy tone to the calling line, and aspecial signalling current connected directly to one winding of saidline relay and to one speaking conductor alternately with said busy tonesource inorder to transmit signalling current toward the calling line.

20. In a telephone system including automatic switches for setting upconnections bebetween calling and called lines, a busy tone source and aspecial signalling current, and means operative when a busy line orgroup of lines is encountered by one of said switches in setting up aconnection for connecting the busy tone source to-the two speaking leadsof said switch and for connecting the special signalling current in thedirection of the callductors of said switch and to transmit thesignalling current in the direction of the calling line.

In witness whereof, I hereunto subscribe my name this 31st day ofOctober, A. D., 1927.

JOHN ELLIS OSTLINE. I11 Witness whereof, I hereunto subscribe my namethis 31st day of October, A. 1)., 192-7.

THOMAS H. RAYNER. In witness whereof, I hereunto subscribe my name this31st day of October, A. D., 1927.

THOMAS PHILIP PREIST.

